1. Field of the Invention
The present invention relates generally to a control apparatus of a transfer mechanism and more particularly to a control apparatus of a transfer mechanism attached to a vehicle in which front and rear wheel drive is attained.
2. Description of the Prior Art
When a vehicle is turned, the turning radius of the front wheel is different from the turning radius of the rear wheel so that a difference in the rotational number is produced between the rotational numbers of the front wheel axle and the rear wheel axle.
Even when a vehicle goes straight, a difference between the effective diameters of the front and rear wheels is produced according to the difference between the air pressures of the respective tires, and a difference between the rotational numbers of the front and rear wheel axles is produced by the difference between the distances from the vehicle body to the road surface as a result of an uneven road surface.
Accordingly, a torque distribution to the front and rear output axles of a transfer mechanism is accomplished by means of a differential gear mechanism.
Generally, there are two types of differential gear mechanisms which are known as a bevel gear type and a planetary gear type. The planetary gear type is superior to the bevel gear type because a torque distribution ratio to the front and rear output axles can be voluntarily set up.
Various necessary conditions should be satisfied by a transfer mechanism so as to correspond to a running state of a vehicle such for example as; a direct condition of the front and rear output axles should be obtained, the torque distribution to the output axle of the front wheel side should be capable of being cut off, a speed changing function should be provided, and it is desirous that the transfer mechanism be of small size, light weight and inexpensive.
Conventionally, an excellent transfer mechanism is provided wherein a carrier of a simple planetary gear mechanism is integrally connected to an output gear which receives a torque from an input axle and an output axle of the rear wheel side and is integrally connected to a ring gear of the simple planetary gear mechanism, and a sun gear thereof is selectively connected to an output axle of the front wheel side or a fixing member or the output axle of the front wheel side and an output gear.
However such a transfer mechanism is not so constructed that a control apparatus for changing the connection between the sun gear and the output axle of the front wheel side or the fixing member or the output gear is suited at a desired shift pattern.
That is, in the conventional apparatus the rear wheel drive position (the sun gear is connected to the fixing member) is located between the four wheel drive position (the sun gear is connected to the output axle of front wheel side) and the direct connecting position of both output axles (the sun gear is connected to the output axle of the front wheel side and the output gear) but since the frequency of shift operation of the rear wheel drive position and the four wheel drive position is more than the direct connecting position of both output axles, it is desirable that the direct connecting position of both output axles and the rear wheel drive position be separately arranged at both sides of the four wheel drive position.